LIQUID-CHROMATOGRAPHIC DETERMINATION OF THE MACROLIDE ANTIBIOTICS ROXITHROMYCIN AND CLARITHROMYCIN IN PLASMA BY AUTOMATED SOLID-PHASE EXTRACTION AND ELECTROCHEMICAL DETECTION

A liquid chromatographic method for the determination of the macrolide antibiotics, roxithromycin and clarithromycin, in plasma is described. The method is fully automated, employing on-line solid-phase extraction for sample clean-up, using the Prospekt unit. Plasma samples, mixed with internal standard, were injected onto exchangeable CN cartridges. After washing, the compounds were eluted and transferred to a C-18 analytical column for separation and electrochemical detection. Clarithromycin was used as internal standard when assaying roxithromycin and vice versa. The recovery of the solid-phase extraction method was 90% and higher, and the relative standard deviation was about 3%. The limit of quantitation was 0.5 mu mol/l when 25 mu l of plasma was injected. Comparison with a liquid-liquid extraction method for sample clean-up showed good agreement.